1. Field of the Invention
The present invention relates to a method of and an apparatus for winding a web around a core.
2. Description of the Related Art
It has been known in the art to wind a web such as an elongate film or sheet of paper around a core to produce a high-quality roll which is free of wrinkles and edge undulations or irregularities by winding the web in intimate contact with a contact pressure roller to prevent air from being entrapped in the web as it is wound, thus producing the roll in a well wound state (see Japanese laid-open patent publication No. 11-59985).
According to the known process, since the contact pressure roller is held in direct contact with the web, it tends to degrade the quality of the web particularly if the web is a delicate material such as a film.
There has been proposed in the art a process of winding a web in a manner to prevent the quality of the web from being lowered and also to prevent the web from developing wrinkles. According to the proposed process, the web is wound under a low tension which is 70% or less of the basic winding tension in an initial web winding stage, and, when the number of turns of the web becomes 1/10 of the number of turns which is to be finally achieved, the winding tension is sharply returned to the high tension, after which the web is wound under a progressively decreasing tension (see Japanese laid-open patent publication No. 60-112562).
The above proposed process is disadvantageous in that since the winding tension is sharply changed from the low tension to the high tension, the web is subjected to an excessive load and liable to be deteriorated under the excessive load applied thereto. Furthermore, as shown in FIG. 22 of the accompanying drawings, because possible deformation of a core a around which a web f is wound is not taken into account, an end face b of the wound web f may possibly develop edge undulations or irregularities depending on the tension which is applied to the web d while it is being wound. Specifically, if the web a is curved while the web f is being wound, the web f is shifted axially of the core a, producing edge undulations or irregularities on the end face b. Such edge undulations or irregularities cause variations in the width L of the produced roll. Therefore, when the roll is supplied to a subsequent process of packaging the roll in a light-shielded state, the roll may not be packaged well in the light-shielded state for desired performance and may possibly suffer fogging due to exposure to light. In addition, the roll may not well fit an image forming apparatus such as an image setter or the like, e.g., may not be inserted into a magazine which is to be loaded into the image forming apparatus.
A film rewinding machine for automatically winding an elongate film on a core and a cutting machine for cutting a wide raw film into an elongate film of given width and then automatically winding the elongate film on a core employ a winding mechanism for supporting the elongate film on the outer circumferential surface of the core when the core is rotated in a winding position.
As disclosed in Japanese patent publication No. 57-40052 (hereinafter referred to as “prior art 1”), the winding mechanism has a holder for holding a spool, angularly movably mounted on the distal end of a belt wrapper, and an actuating mechanism for reciprocally moving the belt wrapper until the central axis of the spool held by the holder is aligned with the central axis of a winding barrel.
A strip coiler disclosed in Japanese utility model publication No. 48-38149 (hereinafter referred to as “prior art 2”) comprises a mandrel for winding a strip as a coil, a plurality of wrapper rolls and wrapper roll plates disposed around the mandrel, and a fluid pressure cylinder for pressing the wrapper rolls into and retracting the wrapper rolls from a position to start winding the strip.
According to the prior art 1, the belt wrapper has an opening aligned with the direction in which the film enters, i.e., the direction in which the film tension acts. Therefore, when the elongate film is wound around the core (spool), the core may possibly be greatly flexed under the film tension. If the core is flexed, then the film tension concentrates on the opposite edges of the core, causing the elongate film to run unstably and disturbing the wound configuration of the elongate film.
According to the prior art 2, the strip coiler is designed for the purpose of setting a gap between the mandrel (corresponding to the core) and each wrapper roll depending on the thickness of the strip (corresponding to the elongate film) to be wound in order to keep the strip as it starts to be wound in a good coil configuration. The strip coiler has nothing incorporated therein for preventing the mandrel from being flexed under the strip tension. Stated otherwise, no consideration is given to achieving a balance between the strip tension and the force to press the wrapper rolls, and hence the strip tension tends to act on the mandrel to cause the mandrel to be flexed.
According to the prior art 2, furthermore, gaps are provided between the mandrel and the wrapper rolls and wrapper roll plates, and the strip is wound on the mandrel through the gaps. However, when the elongate film is wound around the core in this manner, the elongate film has difficulty in being held in intimate contact with the outer circumferential surface of the core, and the wound configuration becomes unstable on the end faces of the wound film roll.